This application is based on Japanese Patent Application HEI 11-287337 filed on Oct. 7, 1999, all the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a solid-state image pickup device, a method of controlling the same, a solid-state image pickup apparatus such as a still camera including a monitor screen, and a method of controlling the same.
In this specification, one transfer stage is defined as a minimum unit of an electric charge transfer region to which electric charge is transferred when a plurality of pulse signals having different phases are applied to charge transfer electrodes successively disposed on a charge transfer path.
For example, when charge in the charge transfer path is driven by signals having four phases, four pulse signals having mutually different phases are respectively applied to four charge transfer electrodes successively arranged on the charge transfer path. In this operation, a region to which electric charge is transferred is referred to as one transfer stage. For example, in the four-phase driving, a region in which four charge transfer electrodes are disposed is called one transfer stage.
In an n-phase driving operation (n is an integer equal to or more than two), a region in which n successive charge transfer electrodes are arranged is referred to as one transfer stage.
2. Description of the Related Art
FIG. 41 shows in a plan view a general configuration of a solid-state image. pickup device.
A solid-state image pickup device X of FIG. 41 includes a semiconductor substrate 101, a plurality of photoelectric converter elements 103 arranged in a row direction and in a column direction on a two-dimensional plane of a surface of the substrate 101, a plurality of vertical charge transfer paths 105 for reading out signal charge accumulated in the photoelectric converter elements 103 and for sequentially transferring the charge in the column direction, a horizontal charge transfer path 107 connected to an end section of each of the vertical charge transfer paths 105 for transferring in a horizontal direction the charge transferred from the vertical charge transfer paths 105, and an output amplifier 111 for amplifying the charge transferred from the horizontal charge transfer path 105 and for outputting charge resultant from the amplification to an external device.
The device X further includes a readout gate 103a between the photoelectric converter 103 and the vertical charge transfer path 105 to read charge from the converter 103 to the path 105.
FIG. 42 shows a cross-sectional view of the horizontal charge transfer path 107.
The path 107 includes a p-type well layer 108 formed in the semiconductor substrate 101, an n-type conductor layer 118 manufactured in the layer 108, and two layers of polycrystalline silicon including a first polycrystalline silicon layer and a second polycrystalline silicon layer fabricated on the substrate 101.
The n-type conductor layer 118 includes a region 118a having a low concentration of n-type impurity and a region 118b having a high concentration of n-type impurity in an alternate fashion. The low-concentration region 118a forms a potential barrier B having high potential energy and the high-concentration region 118b constitutes a potential well W having low potential energy.
The potential barrier and the potential well are alternately disposed in a horizontal direction. One set including one of the potential barriers and one of the potential wells forms one charge transfer unit (to be referred to as one packet herebelow). A large number of packets are manufactured in the horizontal direction.
On the low-concentration region 118a, polycrystalline silicon electrodes (horizontal transfer electrodes 121-0, 121-2, 121-4, etc.) are fabricated in a first layer, and polycrystalline silicon electrodes (horizontal transfer electrodes 121-1, 121-3, 121-5, etc.) are formed in a second layer.
The electrode 121-0 is connected to the electrode 121-1, and a voltage waveform xcfx861 is applied thereto. The electrode 121-2 is connected to the electrode 121-3, and a voltage waveform xcfx862 is applied thereto. Similarly, the electrode 121-4 is connected to the electrode 121-5, and a voltage waveform xcfx861 is applied thereto.
FIG. 43 is a plan view primarily showing a layout of the vertical charge transfer electrodes.
This layout includes four vertical charge transfer electrodes EV, i.e., EV1 to EV4 in a vertical direction for first one of the photoelectric converters 103 arranged in a column direction. For each of second and third ones of the converters 103 sandwiching the first one converter 103 therebetween, four vertical charge transfer electrodes E5 to E8 are disposed.
For the vertical charge transfer electrodes EV1 to EV8, there are further included a driving circuit, not shown, to apply voltage waveforms V1 to V8 to the respective vertical charge transfer electrodes EV1 to EV8.
The voltage waveforms V1 to V4 (or, V5 to V8) are controlled, for example, as follows. To form a potential barrier B in the vertical charge transfer path 105, 0 V is applied to the vertical charge transfer electrodes; to form a potential well W in the vertical charge transfer path 105, 8 V are applied thereto; and to read electric charge from the photoelectric converter 103, 15 V are applied thereto.
The vertical charge transfer path 105 is electrically linked with a region of the horizontal charge transfer path 107 in which one potential well W is formed for each packet.
Referring now to FIGS. 43, 44A to 44C, and 45A to 45C, description will be given of operation of the solid-state image pickup device X.
Assume that the vertical charge transfer electrodes are first set as EV1=0 V, EV2=8 V, EV3=8 V, and EV4=0 V to thereafter set the electrode V3 to 15 V.
As shown in FIG. 44A, charge accumulated in the photoelectric converters 103 is read therefrom via the transfer gate 103a to the vertical charge transfer path 105. The electrode E3 is then restored to 8 V.
As can be seen from FIG. 44B, all charge read out to the transfer path 105 is transferred one transfer stage in the vertical direction to the horizontal charge transfer path 107.
Description will now be given in detail of the operation to transfer charge through the vertical charge transfer path 105 in a step of one transfer stage, i.e., in a stage-by-stage way.
The vertical charge transfer electrode EV4 is set to 8 V. Charge is distributed to regions below the vertical charge transfer electrodes EV2 to EV4.
Thereafter, the transfer electrode EV2 is set to 0 V. Charge is confined in a semiconductor region below the transfer electrodes EV3 and EV4.
When the transfer electrode EV5 (EV1) is set to 8 V, charge is dispersed in a semiconductor region below the transfer electrodes EV3 to EV5.
When the transfer electrode EV 3 is set to 0 V, charge is confined in a semiconductor region below the electrodes EV4 and EV5.
When the electrodes EV6 (EV2) and EV4 (EV8) are respectively set to 8 V and 0 V, charge is accumulated in a semiconductor region below the electrodes EV5 and EV6.
Charge read from one photoelectric converter 103 to the transfer stage 41 of the vertical charge transfer path 105 contiguous to the horizontal charge transfer path 107 in the vertical direction is fed to the transfer path 107.
As shown in FIG. 44C, the charge fed to the transfer path 107 is then transferred through the path 107 and is outputted to an external device.
The operation above is thereafter conducted such that the charge read out to the vertical charge transfer path 105 is again transferred one transfer stage 141 in the vertical direction to the horizontal charge transfer path 107.
The electric charge read out to the transfer stage 141 of the vertical charge transfer path 105 contiguous to the horizontal charge transfer path 107 in the vertical direction is transferred to the transfer path 107. The charge is then horizontally delivered through the path 107 to be fed to an external device.
By repeatedly conducting the operation above, the electric charge can be read from all pixels of the solid-state image pickup device X. That is, an overall pixel readout operation is achieved.
The overall pixel readout method allows a maximum value for resolution in the solid-state image pickup device, for example, a digital still camera and hence is suitable for the reproduction of still pictures with high quality.
As the number of pixels of the solid-state image pickup device increases, a period of time to read out image signals of one frame becomes longer. In a digital still camera conforming to standards of the national television system committee (NTSC), a frame rate of image signals is, for example, one frame per {fraction (1/30)} seconds.
To reproduce a still picture shot by a digital camera, even when the time to read out image signals is increased, there does not arise any serious problem.
However, for a liquid-crystal display disposed in a digital still camera to monitor an image before the image is actually shot, it is required to increase the period of mobile pictures to display mobile pictures in a realtime fashion. That is, in an operation to display a mobile picture (to be referred to as a mobile picture in a movie mode herebelow), when the number of pixels increases, the system cannot achieve the operation according to the frame rate in some cases.
Particularly, when the total number of pixels exceeds one million in the solid-state image pickup device, it is difficult to read image signals from all pixels in the frame rate of {fraction (1/30)} sec. and hence the monitor picture becomes obscure.
To overcome this difficulty, the charge is read from the photoelectric converters 103 to the vertical charge transfer paths 105, for example, as shown in FIGS. 45A to 45C by thinning out signal charge at an equal interval in the vertical direction. By transferring only the charge thus thinned out, the display period (readout period) can be increased to display mobile pictures by a thinning readout operation.
In the thinning readout operation, the system does not read the charge from all photoelectric converters 103 arranged in the column direction, but reads, for example, the charge from every second row of the photoelectric converters arranged adjacent to each other in the vertical direction and feeds the obtained charge to the vertical charge transfer path 105 as shown in FIG. 45A (the charge thus attained is indicated by a negative sign in a small circle in FIGS. 45A to 45C).
As can be seen from FIG. 45B, the charge read out to the vertical charge transfer path 105 is vertically transferred-toward the horizontal charge transfer path 107 in a similar way.
As shown in FIG. 45C, the charge of one photoelectric converter 103 fed to the transfer path 107 is then horizontally transferred through the path 107.
Description has been given of the charge indicated by a negative sign in a small circle. It is also possible that the charge thinned out in the preceding operation, indicated by an open circle in FIG. 45, is read by the thinning readout operation and is fed to the transfer path 105. The charge is then similarly transferred to the transfer path 107.
In the thinning readout described above, the picture obtained from the photoelectric converters has a maximum sensitivity substantially equal to a signal accumulation period which is a readout period. That is, the quicker the display period is, the lower the maximum sensitivity is.
Even if the object to be shot is dark, when a flashlight is used in a final shooting operation (in a still picture reproduction mode using the overall pixel readout), it is possible to obtain sufficient intensity of illumination for the object.
However, the monitor image is used to observe and to determine an object before the object is actually shot. Therefore, peripheral areas of the object remain dark in the observation of the monitor image. This leads to a problem that a moment of a good picture is possibly lost and/or a desired final picture cannot be easily attained.
It is therefore an object of the present invention to provide a solid-state image pickup device, a method of controlling the same, and a solid-state image pickup apparatus using the same in which in the movie mode to display mobile pictures, the display sensitivity is improved and a clear image can be obtained even for a dark object.
According to one aspect of the present invention, there is provided a solid-state image pickup device comprising a plurality of photoelectric converter elements arranged in columns in a vertical direction with a predetermined pitch and in rows in a horizontal direction with a predetermined pitch on a two-dimensional plane; a plurality of vertical charge transfer paths respectively fabricated adjacent to the columns of said photoelectric converter elements, each said path including a plurality of charge transfer stages; a plurality of vertical charge transfer electrodes fabricated on each said vertical charge transfer paths for transferring charge through said each vertical charge transfer path one said charge transfer stage in each transfer period; a horizontal charge transfer path fabricated to be connected to an end section of each said vertical charge transfer path for receiving charge transferred from said vertical charge transfer path and for transferring the charge in a horizontal direction; a plurality of horizontal charge transfer electrodes fabricated on said horizontal charge transfer path in a horizontal direction; an output amplifier fabricated to be connected to an end section of said horizontal charge transfer path for amplifying charge supplied from said horizontal charge transfer path and for outputting charge resultant from the amplification to an external device; and a control circuit operating in a two driving modes including a thinning readout mode and an adding movie mode, said control circuit reading, in the thinning readout mode, charge from said photoelectric converter elements to only part of said charge transfer stages, said control circuit transferring the charge from said vertical charge transfer path to said horizontal charge transfer path, said control circuit reading, in the adding movie mode, charge from said photoelectric converter elements to all said charge transfer stages, said control circuit transferring the charge of at least two said photoelectric converter elements from said vertical charge transfer path to said horizontal charge transfer path to add each said charge to each other, said control circuit stopping a transfer of charge from said vertical charge transfer path to said horizontal charge transfer path, said control circuit outputting by said horizontal charge transfer path charge resultant from the addition to an-external device.
According to one aspect of the present invention, there is provided a solid-state image pickup apparatus, comprising: a plurality of photoelectric. converter elements arranged in columns in a vertical direction with a predetermined pitch and in rows in a horizontal direction with a predetermined pitch on a two-dimensional plane; a plurality of vertical charge transfer paths respectively fabricated adjacent to the columns of said photoelectric converter elements, each said path including a plurality of charge transfer stages; a plurality of vertical charge transfer electrodes fabricated on each said vertical charge transfer paths for transferring charge through said each vertical charge transfer path one said charge transfer stage in each transfer period; a horizontal charge transfer path fabricated to be connected to an end section of each said vertical charge transfer path for receiving charge transferred from said vertical charge transfer path and for transferring the charge in a horizontal direction;
a plurality of horizontal charge transfer electrodes fabricated on said horizontal charge transfer path in a horizontal direction; an output amplifier fabricated to be connected to an end section of said horizontal charge transfer path for amplifying charge supplied from said horizontal charge transfer path and for outputting charge resultant from the amplification to an external device; and
a control circuit operating in a two driving modes including a thinning readout mode and an adding movie mode, said control circuit reading, in the thinning readout mode, charge from said photoelectric converter elements to only part of said charge transfer stages, said control circuit transferring the charge from said vertical charge transfer path to said horizontal charge transfer path, said control circuit reading, in the adding movie mode, charge from said photoelectric converter elements to all said charge transfer stages, said control circuit transferring the charge of at least two said photoelectric converter elements from said vertical charge transfer path to said horizontal charge transfer path to add each said charge to each other, said control circuit stopping a transfer of charge from said vertical charge transfer path to said horizontal charge transfer path, said control circuit outputting by said horizontal charge transfer path charge resultant from the addition to an external device; an optical lens; an iris mechanism for controlling a quantity of light for exposure; a mobile picture monitor display for displaying a shooting object when necessary; a light monitor for measuring brightness of a peripheral area of the shooting object; and a switch responsive to a result of the measurement by said light monitor for automatically selecting, when the brightness of the peripheral area of the shooting object exceeds a reference value, driving of the device in the thinning readout mode and for automatically selecting, when the brightness of the peripheral area of the shooting object is less than a reference value, driving of the device in the adding movie mode.
According to one aspect of the present invention, there is provided a method of controlling a solid-state image pickup apparatus comprising a solid-state image pickup device including a plurality of photoelectric converter elements arranged in columns in a vertical direction with a predetermined pitch and in rows in a horizontal direction with a predetermined pitch on a two-dimensional plane, a plurality of vertical charge transfer paths respectively fabricated adjacent to the columns of said photoelectric converter elements, each said path including a plurality of charge transfer stages; n vertical charge transfer electrodes (n is an integer equal to or more than three) vertically fabricated for each said charge transfer stage on each said vertical charge transfer path, a horizontal charge transfer path fabricated to be connected to a lower end section of a plurality of said vertical charge transfer paths for receiving charge transferred from said vertical charge transfer paths and for transferring the charge in a horizontal direction, an output amplifier fabricated to be connected to an end section of said horizontal charge transfer path for amplifying charge supplied from said horizontal charge transfer path and for outputting charge resultant from the amplification to an external device, and a driving circuit including a timing generator for generating driving pulse signals to said vertical charge transfer paths to drive said solid-state image pickup device; an optical lens, an iris mechanism, a mobile picture monitor display for displaying a shooting object, a light monitor for measuring brightness of a peripheral area of the shooting object, and a shooting method switch for changing a shooting method according to an output from said light monitor, comprising the steps of: a) setting the apparatus to a movie mode and for displaying a monitor image on the mobile picture monitor display; b) measuring by the light monitor a quantity of light in peripheral area of the shooting object and selecting, when the quantity of light measured exceeds a reference value, a thinning readout mode in which the charge of said photoelectric converters read out to only part of said charge transfer stages is read out to said vertical charge transfer path associated therewith and is transferred from said vertical charge transfer path to said horizontal charge transfer path, and selecting, when the quantity of light measured is less than a reference value, an adding movie mode in which the charge is read out to all said charge transfer stages, the charge of at least two said photoelectric converters is transferred from said vertical charge transfer path to said horizontal charge transfer path, each said charge is added to each other, a transfer of charge from said vertical charge transfer path to said horizontal charge transfer path is stopped, and charge resultant from the addition is transferred and is outputted by said horizontal charge transfer path to an external device; c) transferring the charge fed to said horizontal charge transfer path, amplifying the charge by the output amplifier, and delivering charge resultant from the amplification to an external device; d) repeatedly executing said steps b) and c) and continuously displaying a picture on the monitor display in the thinning readout mode or the adding movie mode; and e) shooting a still picture at a desired point of timing.
According to the solid-state image pickup device (apparatus) of the present invention, even when a shooting object to be shot is, for example, dark, it is possible to obtain a monitor picture or image with high sensitivity to observe an image of the object before the object is finally shot (as a still picture). The user can shoot the image at a suitable moment for a good picture and can readily obtain a desired picture.